When an image is scanned by a multi-channel (e.g. three color band) transducer, such as an RGB video camera, differences in sensitivity and dynamic range of its respective channels cause the camera to produce color representative output signals which are offset from one another in terms of color intensity and which may be clipped or limited near the upper and lower ends of the overall dynamic range of the camera. An example of these differential sensitivity output characteristics is illustrated in FIG. 1, which shows the relationship between light intensity and output response (color representative signals) for the blue and green channels of an RGB color video camera. Differences in absolute sensitivity are typically compensated by a bias adjustment of the camera's channel outputs, so that, for a neutral color (e.g. white), the output level for each channel output should be effectively the same, irrespective of image intensity. However, as noted above, because the dynamic range of each channel is usually not the same, after applying a signal bias adjustment for aligning, or correcting, the channel output characteristics, there is the problem of limited, or clipped, signal levels in the neighborhood of the extreme ends of the operational range, as shown in FIG. 2.
Namely, in the vicinity of the lower intensity (shadow) end of the camera's sensitivity characteristic, blue signals are clipped at an output intensity level 22, before, or higher than, green signals, which are clipped at a lower output intensity level 32, so that the dynamic range of the green response characteristic extends over a region 33 that falls below the blue intensity level 22. As a consequence, when the scanned image is reconstructed, for example, by way of a RGB color print machine, regions of low intensity (shadows) are blue-colored, rather than neutral, thereby degrading the quality of the reproduced image. Similarly, at the upper, highlight end of the camera's operational range, because the green response characteristic is clipped at an intensity level 34, above which the blue characteristic varies over region 23 to an upper limit at level 24, the blue signal predominates, thus causing highlights to be blue-tinged.